Because the damage effects of explosive weapons decrease with distance due to an inverse cube law, even modest improvements in accuracy (hence reduction in miss distance) enable a target to be attacked with fewer or smaller bombs. Thus, even if some guided bombs miss, fewer air crews are put at risk and the harm to civilians and the amount of collateral damage may be reduced.

The advent of precision-guided munitions resulted in the renaming of older bombs "unguided bombs", "dumb bombs", or "iron bombs".

Radio-controlled weapons

The Germans were first to introduce PGMs in combat, with KG 100 deploying the 1,400-kg (3,100-lb) MCLOS-guidance Fritz X armored gravity ordnance, to successfully attack the Italian battleshipRoma in 1943 and sink a hospital ship at Anzio[citation needed], and the similarly MCLOS-guided Henschel Hs 293 rocket-boosted glide missile (also in use since 1943, but only against lightly armored or unarmored ship targets). The closest Allied equivalents were the 1,000-lb (454-kg) VB-1 AZON (AZimuth ONly), used in both Europe and the CBI theater, and the US Navy's Bat, primarily used in the Pacific Theater of World War II—the Navy's Bat had its own on board, autonomous radar seeker system to direct it to a target. In addition, the U.S. tested the rocket-propelled Gargoyle, which never entered service.[4] Japanese PGMs—with the exception of the anti-ship air-launched, rocket-powered, human-piloted Ohka suicide flying bomb—did not see combat in World War II.[5]

Prior to the war, the British experimented with radio-controlled remotely guided planes laden with explosive, such as Larynx. The United States Army Air Forces used similar techniques with Operation Aphrodite, but had few successes; the German Mistel (Mistletoe) "parasite aircraft" was no more effective, guided by the human pilot flying the single-engined fighter mounted above the unmanned, explosive-laden twin engined "flying bomb" below it, released in the Mistel's attack dive from the fighter.

The U.S. programs restarted in the Korean War. In the 1960s, the electro-optical bomb (or camera bomb) was reintroduced. They were equipped with television cameras and flare sights, by which the bomb would be steered until the flare superimposed the target. The camera bombs transmitted a "bomb's eye view" of the target back to a controlling aircraft. An operator in this aircraft then transmitted control signals to steerable fins fitted to the bomb. Such weapons were used increasingly by the USAF in the last few years of the Vietnam War because the political climate was increasingly intolerant of civilian casualties, and because it was possible to strike difficult targets (such as bridges) effectively with a single mission; the Thanh Hoa Bridge, for instance, was attacked repeatedly with iron bombs, to no effect, only to be dropped in one mission with PGMs.

Infrared-guided/electro-optical weapons

In World War II, the U.S. National Defense Research Committee developed the VB-6 Felix, which used infrared to home on ships. While it entered production in 1945, it was never employed operationally.[6] Precision guidance has been applied to weapons other than conventional bomb warheads. The RaytheonMaverick heavy anti-tank missile has among its various marks guidance systems such as electro-optical (AGM-65A), imaging infra-red (AGM-65D), and laser homing (AGM-65E).[7] The first two, by guiding themselves based on the visual or IR scene of the target, are fire-and-forget in that the pilot can release the weapon and it will guide itself to the target without further input, which allows the delivery aircraft to manoeuvre to escape return fire. The Pakistani NESCOMH-2 MUPSOW and H-4 MUPSOW is an electro-optical (I.R imaging and Television guided) is a drop and forget precision-guided glide bomb. The Israeli Elbit Opher is also an I.R imaging "drop and forget" guided bomb that has been reported to be considerably cheaper than laser-homing bombs and can be used by any aircraft, not requiring specialized wiring for a laser designator or for another aircraft to illuminate the target. During NATO's air campaign in 1999 in Kosovo the new Italian AF AMX employed the Opher.[8]

Laser-guided weapons

Diagram showing the operation of a laser-guided ammunition round. From a CIA report, 1986.

In 1962, the US Army began research into laser guidance systems and by 1967 the USAF had conducted a competitive evaluation leading to full development of the world's first laser-guided bomb, the BOLT-117, in 1968. All such bombs work in much the same way, relying on the target being illuminated, or "painted," by a laser target designator on the ground or on an aircraft. They have the significant disadvantage of not being usable in poor weather where the target illumination cannot be seen, or where a target designator cannot get near the target. The laser designator sends its beam in a coded series of pulses so the bomb cannot be confused by an ordinary laser, and also so multiple designators can operate in reasonable proximity.

Laser-guided weapons did not become commonplace until the advent of the microchip. They made their practical debut in Vietnam, where on 13 May 1972 they were used in the second successful attack on the Thanh Hóa Bridge ("Dragon's Jaw"). This structure had previously been the target of 800 American sorties[9] (using unguided weapons) and was partially destroyed in each of two successful attacks, the other being on 27 April 1972 using Walleyes.

They were used, though not on a large scale, by the British forces during the 1982 Falklands War.[10] The first large-scale use of smart weapons came in the early 1990s during Operation Desert Storm when they were used by coalition forces against Iraq. Even so, most of the air-dropped ordnance used in that war was "dumb," although the percentages are biased by the large use of various (unguided) cluster bombs. Laser-guided weapons were used in large numbers during the 1999 Kosovo War, but their effectiveness was often reduced by the poor weather conditions prevalent in the southern Balkans.

There are two basic families of laser-guided bombs in American (and American-sphere) service: the Paveway II and the Paveway III. The Paveway III guidance system is more aerodynamically efficient and so has a longer range, however it is more expensive. Paveway II 500-pound LGBs (such as GBU-12) are a cheaper lightweight PGM suitable for use against vehicles and other small targets, while a Paveway III 2,000-pound penetrator (such as GBU-24) is a more expensive weapon suitable for use against high-value targets. GBU-12s were used to great effect in the first Gulf War, dropped from F-111F aircraft to destroy Iraqi armored vehicles in a process referred to as "tank plinking."

Ugroza (Russian: Угроза, meaning "menace") is a precision-guided weapons system made in Russian Federation. It is an upgrade for standard Russian "dumb" rockets, including the S-5, S-8, and S-13 rockets.[19][20] The system upgrades the "dumb" rockets with laser guidance, very significantly increasing their accuracy. It requires a laser target designator, from either an airborne or land based source, to "paint" a target. Circular error probable (CEP) is about 0.8 to 1.8 m,[19] while maximum ranges of rockets varies from the rockets used 1.5–8 km.[19] Ugroza allows rockets to be ripple-fired up to 7 at a time. The notable novelty is that the system does not use aerodynamic flight control (e.g. tail fins), but impulse steering with mini-thrusters.[19] It has been dubbed as the Russian concept of impulse corrections (RCIC).[19]

Lessons learned during the first Gulf War showed the value of precision munitions, yet they also highlighted the difficulties in employing them—specifically when visibility of the ground or target from the air was degraded.[21] The problem of poor visibility does not affect satellite-guided weapons such as Joint Direct Attack Munition (JDAM) and Joint Stand-Off Weapon (JSOW), which make use of the United States' GPS system for guidance. This weapon can be employed in all weather conditions, without any need for ground support. Because it is possible to jam GPS, the guidance package reverts to inertial navigation in the event of GPS signal loss. Inertial navigation is significantly less accurate; the JDAM achieves a published Circular Error Probable (CEP) of 13 m under GPS guidance, but typically only 30 m under inertial guidance (with free fall times of 100 seconds or less).[22][23]

The Griffin Laser Guided Bomb (Griffin LGB) is a laser-guided bomb system made by Israel Aerospace Industries' MBT missile division. It is an add-on kit which is used to retrofit existing Mark 82, Mark 83, and Mark 84 and other "dumb fire" gravity bombs, making them into laser-guided smart bombs (with the option of GPS guidance). Initial development completed in 1990. The Griffin conversion kit consists of a front "seeker" section and a set of steerable tailplanes. The resulting guided munition features "trajectory shaping", which allows the bomb to fall along a variety of trajectories – from a shallow angle to a vertical top attack profile. IAI publishes a circular error probable figure for the weapon of 5 metres.[25]

The SMKB (Smart-MK-Bomb) is a Brazilian guidance kit that turns a standard Mk 82 (500 lbs) and Mk 83 (1.000 lbs) into a Precision-guided weapon, respectively called SMKB-82 and SMKB-83. The kit provides extended range up to 50 kilometres (27 nmi) and are guided by an integrated inertial guidance system coupled to three satellites networks, relying on wireless to handle the flow of data between the aircraft and the munition.

FT PGB is a family of Chinese satellite and Inertial, guided munitions.

The precision of these weapons is dependent both on the precision of the measurement system used for location determination and the precision in setting the coordinates of the target. The latter critically depends on intelligence information, not all of which is accurate. According to a CIA report, the accidental United States bombing of the Chinese embassy in Belgrade during Operation Allied Force by NATO aircraft was attributed to faulty target information.[27] However, if the targeting information is accurate, satellite-guided weapons are significantly more likely to achieve a successful strike in any given weather conditions than any other type of precision-guided munition.

Advanced guidance concepts

Responding to after-action reports from pilots who employed laser or satellite guided weapons, Boeing developed a Laser JDAM (LJDAM) to provide both types of guidance in a single kit. Based on the existing Joint Direct Attack Munition configurations, a laser guidance package is added to a GPS/INS-guided weapon to increase its overall accuracy.[28] Raytheon has developed the Enhanced Paveway family, which adds GPS/INS guidance to their Paveway family of laser-guidance packages.[29] These "hybrid" laser and GPS guided weapons permit the carriage of fewer weapons types, while retaining mission flexibility, because these weapons can be employed equally against moving and fixed targets, or targets of opportunity. For instance, a typical weapons load on an F-16 flying in the Iraq War included a single 2,000-lb JDAM and two 1,000-lb LGBs. With LJDAM, and the new GBU-39 Small Diameter Bomb (SDB), these same aircraft can carry more bombs if necessary, and have the option of satellite or laser guidance for each weapon release.

Spice (munition) is an IsraeliEO/GPS-guided guidance kit for converting air-droppable unguided bombs into precision guided bombs. Spice can be preprogrammed, with up to 100 different targets it may have to engage during a mission. The one target it will actually engage may then be selected, inflight, by an aircrewman.

Guided small arms

Precision-guided small arms prototypes have been developed which use a laser designator to guide an electronically actuated bullet to a target.[38] Another system in development uses a laser range finder to trigger an explosive small arms shell in proximity to a target. The U.S. Army plans to use such devices in the future.[39]